Methods for isolating bacteria

ABSTRACT

The present invention relates to compositions and methods to identify novel bacteria and metabolites derived therefrom. More specifically, the invention describes a novel method to isolate bacteria producing metabolites of interest from environmental samples. Particularly, the invention discloses a method to select rare antibiotic producing bacteria. The invention can be used from any sample and allows the isolation of bacteria having e.g., pharmaceutical or agrochemical interest.

CROSS-REFERENCE TO RELATED APPLICATION

This application is the U.S. national stage application of International Patent Application No. PCT/EP2010/050513, filed Jan. 18, 2010, which claims the benefit of U.S. Provisional Patent Application No. 61/145,606, filed Jan. 19, 2009, the disclosures of which are hereby incorporated by reference in their entireties, including all figures, tables and amino acid or nucleic acid sequences.

The present invention relates to compositions and methods to identify novel bacteria and metabolites derived therefrom. More specifically, the invention describes a novel method to isolate bacteria producing metabolites of interest from environmental samples. Particularly, the invention discloses a method to select novel antibiotic producing bacteria. The invention can be used from any sample and allows the isolation of bacteria having e.g., pharmaceutical or agrochemical interest.

BACKGROUND

For time immemorial, mankind has sourced surrounding organisms for therapeutic purposes, and most of the commercial antibiotics still have a natural origin. During the last 10 years, in an effort to rationalize and to speed up antibacterial discovery processes, the industry has moved from natural products and a molecule-oriented discovery strategy to synthetic molecules and a target-oriented strategy.

After years of uniformization of antibiotic R&D process, with an unprecedented high attrition rate, it is necessary to return to natural resources. Indeed, the screening of natural product libraries usually yields a higher percentage of antibiotics hits than that of chemical libraries, and consequently provides a higher probability to obtain a therapeutic. The first reason probably lies in the ecologic role of the antibiotics, which have been optimized through the course of evolution, to defend plants, animals and micro-organisms against other living organisms. Furthermore, natural products are generally as lipophilic as combinatorial compounds, but they have an unparalleled structural diversity and dispersion in chemical space. This helps to find rare hydrophilic hits which can be optimized for in vivo applications.

It is generally assumed that 20 to 30 percent of the bacteria isolated from environmental sources such as soil or water are antibiotics producers (Bérdy, 2005). For obvious reasons, the fitter and the most represented bacteria are the most frequently isolated. This explains why many antibiotics produced by Bacillus or Pseudomonas have already been documented, and why it is more and more difficult to find new molecular entities produced by these genera. Other families of under-represented bacteria, more adapted to antibiotic production, due to a bigger genome, can be easily isolated with adapted techniques. This is the case of actinomycetals, by far the best antibiotic producers (Bérdy, 2005). They were extensively studied by the pharmaceutical industry between 1950 and 1980, and it is now difficult to identify strains producing non-redundant molecules.

In the last decade, efforts have been devoted to isolating rare bacteria in order to find new chemical entities of pharmaceutical interest. Myxobacteria, for example, are known since the 1940's, but due to difficulties encountered for isolating them, they were under-represented in the collections. Thanks to an extensive collection campaign carried out by Reichenbach H and collaborators, so far about 80 different compounds and 450 structural variants produced by Myxobacteria have been characterized (Reichenbach, 2001). Many of those compounds were new. Among them is the antineoplasic drug, epothilones, currently being evaluated in clinical trials.

It is generally recognized, however, that microbiologists are unable to culture most soil microorganisms (Schoenborn et al, 2005). The number of cultivable cells in soil is often only about 1% of the total number of cells present. Most of these bacteria are difficult to detect and isolate using standard isolation techniques, either because they are rare in the environment, or because they are less adapted to environmental conditions than other bacteria like Pseudomonas spp. or Bacillus spp. and are rapidly overgrown. Several isolation techniques aiming to increase the diversity of the isolates have been published. For example, serial liquid dilution culture has been used successfully to improve cultivability (Schoenborn et al, 2005) and to facilitate the isolation of bacteria from diverse environments. Yang et al., 2008, also described the use of microwave treatment to isolate rare actinomycetes. WO02/059351 concerns a method for enriching a microbial population from a natural environment using e.g., hot spring water.

However, environmental microorganisms still represent a rich and unexploited resource of novel compounds and activities, and there is a need in the art for improved or alternative methods to identify bacteria of interest.

SUMMARY OF THE INVENTION

The present application provides a novel approach to identify or isolate bacteria from environmental samples. More particularly, the invention discloses an efficient and rapid method of identifying or isolating rare bacteria from environmental samples using a DNA damaging treatment.

An object of the present invention therefore resides in a method to identify or isolate a (secondary) metabolite producing bacterium, the method comprising subjecting a sample comprising uncharacterized bacteria to a cell destructing DNA damaging treatment and identifying or isolating from said treated sample a bacterium which produces the (secondary) metabolite. In a preferred embodiment, the treatment is a repeated irradiation treatment.

In this respect, a particular object of this invention is a method to identify or isolate a metabolite-producing bacterium, the method comprising:

-   -   a) providing a sample comprising uncharacterized bacteria;     -   b) subjecting the sample to a repeated irradiation treatment;     -   c) identifying or isolating a living or growing bacterium from         said treated sample; and     -   d) selecting a bacterium of step c) which produces the         metabolite.

In a particular embodiment, the treatment comprises a sequential UV treatment, e.g., a repetition of at least 2, preferably 3 or more irradiations at essentially regular intervals.

In a particular embodiment, the treatment comprises a repeated UV irradiation.

According to another particular embodiment, the invention relates to a method to identify or isolate a metabolite-producing bacterium, the method comprising:

-   -   a) providing a sample comprising uncharacterized bacteria;     -   b) adding to the sample an antibiotic of the bleomycin family;     -   c) identifying or isolating a living or growing bacterium from         said treated sample; and     -   d) selecting a bacterium of step c) which produces the         metabolite.

The preferred antibiotic of the bleomycin family is bleocin.

The metabolite may be any pharmaceutical product, such as antibiotics, bacteriostatic compounds, anti-metabolite agents, chemotherapeutic compounds, anti-fungal agents, anti-viral compounds, cytokine-activity compounds or cell-growth factors.

Another object of this invention is a method to identify or isolate a bacterium which produces an antibiotic or a bacteriostatic-compound, the method comprising:

-   -   a) providing a sample comprising uncharacterized bacteria;     -   b) subjecting the sample to a repeated irradiation treatment,         preferably a repeated UV treatment;     -   c) identifying or isolating living or growing bacteria from said         treated sample; and     -   d) exposing identified or isolated bacteria of step c), or an         extract thereof, to a reference bacterial strain and identifying         or isolating a bacterium which exhibits an antibiotic or         bacteriostatic activity.

In a preferred embodiment, the methods of the present invention comprise a further step of isolating or purifying the metabolite produced by said bacterium.

Furthermore, the methods of the invention optionally comprise a further step of modifying, either genetically, biologically or chemically, the identified or isolated bacteria or their DNA by any technical process known per se by a skilled person, said modification aiming to improve e.g., the viability, growth or function of the said bacteria, e.g., in order to improve the antibiotic activity or production. This includes, without limitation, cell fusion, accelerated evolution, DNA shuffling technologies, insertion of eukaryote, prokaryote or synthetic nucleic acid (e.g., DNA) from another strain, or any genetic engineering technology. Said modification step can be carried out on the isolated bacteria, or at any earlier stage of the process, e.g., on the sample of step a), for instance.

Another object of this invention resides in a wild type or modified bacterium obtained by a method as disclosed above, or an extract thereof.

A further object of this invention is a method of producing a metabolite, particularly a pharmaceutical compound, the method comprising (i) identifying or isolating a bacterium which produces said metabolite using the method as defined above and (ii) producing said antibiotic.

A further object of this invention is a method of identifying, isolating or producing a pharmaceutical compound (such as an antibiotic), using a wild type or modified Deinococcus bacterial strain.

A further object of this invention resides in the use of a wild type or modified Deinococcus bacterium to produce a pharmaceutical compound (such as an antibiotic).

A further object of this invention is an antibiotic derived from a wild type or modified Deinococcus bacteria.

A further object of this invention is a method of producing a recombinant host cell, the method comprising identifying or isolating a bacterium according to the method as defined above and cloning one or several genes (or corresponding synthetic or recombinant nucleic acids) from said bacterium in another host cell, thereby producing a recombinant host cell.

The methods of the present invention can be used with various samples, such as environmental samples, and has been used successfully to isolate novel bacteria having advantageous pharmaceutical and/or agro-chemical properties.

LEGEND TO THE FIGURES

FIG. 1: Bacterial mat obtained after: a) 1 exposure to UV: 0, 4 and 17 mJ/cm² and b) repeated exposures to UV treatment of 4 mJ/cm². Dark colonies are D. radiopugnans. The other bacteria belong to soil community.

DETAILED DESCRIPTION OF THE INVENTION

The present application describes a novel method to identify or isolate bacteria from samples. More particularly, the invention discloses an efficient and rapid method of identifying or isolating rare bacteria from environmental samples using a cell destructing DNA damaging treatment.

Resistance of bacteria to UV or radiation has been extensively studied to understand how bacteria can survive in such aggressive environment (Makarova et al, 2001). Rainey et al, 2005, showed that Geodermatophylus spp. and Deinococcus spp. are among the most radiation-resistant bacteria collected from the Sonoran desert soils. Other bacteria were also isolated namely, Deinococcus, Hymenobacter, Kineococcus, Kocuria, and Methylobacterium.

The present invention now proposes the use of a cell destructing DNA damaging treatment to isolate novel (under-represented) bacteria producing metabolites. The present invention indeed shows that such a treatment, which would normally cause substantial cell death, unexpectedly allows the selection of under-represented bacteria having remarkable properties of producing valuable metabolites.

The invention now shows for the first time that, after a cell destructing DNA damaging treatment, it is possible to isolate a high number of bacteria able to produce valuable secondary metabolites.

An object of the present invention therefore resides in a method to identify or isolate a metabolite producing bacterium, the method comprising subjecting a sample comprising uncharacterized bacteria to a cell destructing DNA damaging treatment and identifying or isolating from said treated sample a bacterium which produces the metabolite.

In a particular embodiment, the method comprises:

-   -   a) providing a sample comprising uncharacterized bacteria;     -   b) subjecting the sample to a cell destructing DNA damaging         treatment;     -   c) identifying or isolating a living or growing bacterium from         said treated sample; and     -   d) selecting a bacterium of step c) producing the metabolite.

The method can be implemented with various samples comprising uncharacterized bacteria, particularly with samples which are or derive from an environmental sample. Within the context of this invention, environmental samples include any sample containing (a plurality of) uncharacterized (micro)organisms, particularly uncultivated microorganisms (e.g., microorganisms that have not been purposely cultured and expanded in isolated form). The sample may be obtained or derived from natural environments or from artificial or specifically created environments.

As indicated, the sample may be any environmental sample, such as those obtained or derived from soil, water, vegetal extract, biological material, sediments, peatlands, industrial effluents or sites, mineral extracts, sand, and the like. The sample may be collected from various regions or conditions, such as but not limited to tropical regions, volcanic regions, forests, farms, industrial areas, etc. The sample usually contains various species of (uncharacterized, uncultivated) microorganisms, such as terrestrial microorganisms, marine microorganisms, freshwater microorganisms, symbiotic microorganisms, etc. Species of such environmental microorganisms include bacteria, algae, fungi, yeasts, moulds, viruses, etc. The microorganisms may include extremophile organisms, such as e.g., thermophiles. The sample typically comprises various species of such (uncultivated) microorganisms, as well as various amounts thereof. Furthermore, the sample may contain, in addition, known and/or cultivable microorganisms (e.g., prokaryotic or eukaryotic).

It should be understood that the present invention is not limited to any specific type of sample or environmental microorganism, but can be implemented using any sample comprising uncultivated microorganisms.

In a preferred embodiment, the sample is or derives from soil, water, hot springs, marine environment, mud, wood, stone, moss, vegetal extract, lichen, biological material, sediment, biofilm, industrial effluents, gas, sand, oil, sewage, or animal or human dejection.

For use in the present invention, the sample may be wet, soluble, dry, in the form of a suspension, paste, etc. Furthermore, prior to step b) of the method, the sample may be treated to improve the process, for instance to enrich for microorganisms, e.g., such as through filtration, washings, concentration, dilution, steering, drying, etc.

In a particular embodiment, the sample is in the form of a filtered suspension. More particularly, the sample may be sterile-filtered and/or placed in sterile water, prior to treatment step b).

Step b) of the process comprises subjecting the sample (i.e., microorganisms contained in the sample) to a cell destructing DNA damaging treatment.

The cell destructing DNA damaging treatment designates a treatment that causes substantial cell death in the sample, as opposed to mere mutagenic treatments which introduce DNA modifications. In particular, the cell destructing DNA damaging treatment is a treatment that is sufficient to cause 90% cell death, or more, in a culture of E. coli bacteria. Even more preferably, the cell destructing DNA damaging treatment is a treatment that is sufficient to reduce by at least 2 log the bacterial titer in a culture of E. coli. Surprisingly, the invention shows that such a treatment, which would normally be lethal to most cell populations, allows the efficient and rapid isolation of novel microorganisms from various types of samples, which microorganisms produce valuable (secondary) metabolites. This result is particularly surprising since subjecting microorganisms to such cell destructing DNA damaging treatment would have been expected to prevent isolation of living microorganisms. Surprisingly, the invention allows the selection of rare microorganisms from the sample, especially microorganisms having the ability to either reassemble their genome or to resist DNA damage.

The invention thus discloses, for the first time, the use of a cell destructing DNA damaging treatment to select, with a high efficacy, under-represented bacteria producing valuable (secondary) metabolites. As illustrated in the examples, the invention allowed the isolation of novel bacterial strains of Deinococcus sp, Bacillus sp, Methylobacterium sp. Sphingobacterium sp. Cellulosimicrobium sp. Tepidimonas sp. Truepera sp., Porphyrobacter sp., Novosphingobium sp., Exiguobacterium sp., Nocardia sp Arthrobacter sp., Rhodococcus sp., Microbacterium sp., Kineococcus sp., and Williamsia sp.

The DNA damaging treatment may comprise subjecting the sample to irradiation(s) and/or to one or several genotoxic agents. The treatment is conducted under conditions and/or for a period of time sufficient to induce substantial cell death in the microorganisms present in the sample.

In a preferred embodiment, the DNA damaging treatment comprises subjecting the sample to one or several irradiations. A preferred treatment comprises subjecting the sample (i.e., microorganisms in the sample) to a repeated (e.g., sequential) irradiation treatment.

Irradiation may be selected from UV, gamma and/or X ray irradiation, either alone or in combinations, most preferably UV irradiation(s). Irradiation treatment typically comprises subjecting the microorganisms to one or several sequential irradiations (e.g., from 1 to 5), which may be of the same or different nature, preferably of the same nature. Repeated irradiation treatments are typically carried out at an interval of between 1 and 8 hours, preferably 3 to 5 hours, and more preferably of about 4 hours.

A particularly preferred treatment comprises subjecting the sample to a cell destructing UV irradiation. The invention indeed shows that such a treatment allows to isolate with high efficacy from environmental (e.g., soil or water) samples, under-represented bacteria species producing (secondary) metabolites (such as antibiotics). Cell destructing UV treatments are typically of between 0.5 and 400 mJ/cm2, more preferably of between 1 and 200 mJ/cm2, typically between 1 and 100 mJ/cm2, applied for a period of time of about 5″ to 5′. A preferred UV treatment is 4 mJ/cm2 for 30 seconds.

In a specific embodiment, the cell destructing DNA damaging treatment comprises subjecting the sample to at least 2, preferably at least 3 UV treatments of between 0.5 and 400 mJ/cm2 each, preferably of about 4 mJ/cm2 each, carried out at an interval of between 1 and 8 hours, preferably 3 to 5 hours, and more preferably of about 4 hours.

In an alternative method, the cell destructing DNA damaging treatment comprises contacting the sample with a genotoxic agent, such as a solvent, mitomycin, a bleomycin antibiotic, or H₂O₂. It should be understood that genotoxic agents may also be used in combination with irradiation. In a particular embodiment, the treatment step b) comprises adding to the sample an effective amount of bleocin, a bleomycin family antibiotic. As illustrated in the examples, the addition of bleocin causes substantial bacterial cell death while allowing rare, metabolite-producing bacteria to grow.

During the treatment phase, the sample is preferably placed in a suitable culture medium such as, without limitation, PGY (Bacto-peptone 10 g/L, Yeast extract 5 g/L, glucose 20 g/L) or LB (Bacto-tryptone 10 g/L, Yeast extract 2.5 g/L, Sodium chloride 10 g/L). It should be understood that other suitable culture media are known to the skilled person (Buchanan et al, 1974, Difco, 1995)) or may be prepared by the skilled person from such known media.

Treatment step b) is typically performed in a solid or semi-solid culture medium, such as in the presence of a gel (e.g., agar). A most preferred treatment medium comprises an agar culture medium, such as a soft agar culture medium. In a particular embodiment, a TGY agar medium is used to grow the bacteria. However, different solid media containing a carbon source, a nitrogen source and mineral salts can be used as well. Serial dilution techniques can also be used according to Schoenborn et al 2004.

In step c), living or growing bacteria are identified or isolated from the treated sample. Living or growing bacteria may be identified by different means known per se in the art. In a particular embodiment, colonies which form in the culture media are identified. The living or growing bacteria can be isolated and placed in fresh medium for further culture or expansion.

As mentioned above, the method of this invention preferably comprises a step d) of selecting one or several bacteria, from the identified or isolated living or growing bacteria, which produce a particular metabolite. In this regard, it should be noted that steps c) and d) can be performed sequentially, in any order, or simultaneously. For instance, the bacteria in the sample may be placed under conditions suitable to select the desired activity in step b) or c), so that growing or living bacteria identified or isolated in step c) exhibit the desired activity. Alternatively, the bacteria identified or isolated in step c) may be placed under conditions suitable to select the desired activity in step d) only, so that growing or living bacteria are first identified or isolated in step c) and then selected for the desired activity.

The metabolite may be any compound having pharmaceutical and/or agro-chemical interest. In a particular embodiment, the metabolite is a pharmaceutical compound (for use in human or veterinary medicine), preferably selected from antibiotics, bacteriostatic compounds, anti-metabolite, chemotherapeutic compounds, anti-parasitic agents, anti-fungal agents, anti-viral compounds, cytokine-activity compounds or cell-growth factors.

The metabolite may also have utility e.g., in cosmetics or agriculture, such as pigments, insecticides, pesticides, chemical-degrading compounds, etc.

The selection or identification or bacteria producing the selected metabolite can be made according to techniques known per se in the art. In a particular embodiment, step d) comprises exposing identified or isolated bacteria of step c), or an extract thereof, to one or several indicator cells and selecting a bacterium which affect the viability, growth, metabolism, mobility, RNA expression, protein expression, protein secretion or virus production of at least one of said indicator cells.

In the case of antibiotic or antibiostatic agents, the indicator cells are typically reference bacterial strains and test bacteria which inhibit the growth or kill said reference strains are selected.

In the case of, e.g., anti-viral compounds, the indicator cells are typically virus-producing cells and bacteria which affect the production of virus or viability of virus-infected cells are selected.

In this regard, in a particular embodiment, the method of the invention further comprises a step of isolating or purifying the metabolite produced by said bacteria.

In a preferred embodiment, the selected activity is the production of an antibiotic or bacteriostatic activity. The present invention shows that antibiotic-producing bacteria can be isolated with high efficiency from environmental samples treated according to the present method. More particularly, as illustrated in the examples, antibiotic-producing bacteria of the genus Bacillus, Methylobacterium, Sphingobacterium, Cellulosimicrobium, Tepidimonas, Nocardia, Deinococcus, Truepera, Porphyrobacter sp., Novosphingobium sp., Exiguobacterium sp., Chromobacterium sp, Arthrobacter sp, Rhodococcus sp, Microbacterium sp, Kineococcus sp, or Williamsia sp have been isolated from different environmental samples, including water, soil, animal dejection, wood, etc.

The selection of bacteria which produce antibiotics can be performed using different techniques known per se in the art (Singh, 2008, Janssen, 2002, Hamaki, 2005, Schoenborn L. et al. 2005). In a particular embodiment, the tested bacteria (or an extract thereof) are placed in contact with one or several reference bacterial strains, and the ability of the test bacteria to inhibit the growth of or to kill the reference strains is measured, as an indication of the antibiotic activity. Examples of reference strains include, without limitation, E. coli, Staphylococcus aureus, or Candida tropicalis (Lorian, 1996).

In this regard, the invention relates to a method to identify or isolate bacteria producing an antibiotic or bacteriostatic agent, the method comprising:

-   -   a) providing a sample comprising uncharacterized bacteria;     -   b) subjecting the sample to a cell destructing DNA damaging         treatment, preferably a repeated irradiation treatment, e.g., an         UV treatment;     -   c) identifying or isolating living or growing bacteria from said         treated sample; and     -   d) exposing identified or isolated bacteria of step c), or an         extract thereof, to a reference bacterial strain and identifying         or isolating bacteria which exhibit an antibiotic or         bacteriostatic activity.

The method may further comprise a step of isolating or purifying the antibiotic produced by said bacteria.

A further object of this invention is a method to identify or isolate anti-metabolite or chemotherapeutic or anti-fungal or cytokine activity or cell-growth factor producing bacteria, the method comprising:

-   -   a) providing a sample comprising uncharacterized bacteria;     -   b) subjecting the sample to a cell destructing DNA damaging         treatment, preferably a repeated irradiation treatment, e.g., an         UV treatment;     -   c) identifying or isolating living or growing bacteria from said         treated sample; and     -   d) exposing identified or isolated bacteria of step c), or an         extract thereof, to one or several reference eukaryotic cell         types and identifying selected bacteria which affect the         viability, growth, metabolism, mobility, RNA expression, protein         expression, or protein secretion of some of the eukaryotic cell         types.

The method may further comprise a step of isolating or purifying the anti-metabolite or chemotherapeutic or anti-fungal or cytokine activity or cell-growth factor produced by said bacteria.

A further object of the invention resides in a method to identify or isolate anti-viral compound producing bacteria, the method comprising:

-   -   a) providing a sample comprising uncharacterized bacteria;     -   b) subjecting the sample to a cell destructing DNA damaging         treatment, preferably a repeated irradiation treatment, e.g., an         UV treatment;     -   c) identifying or isolating living or growing bacteria from said         treated sample; and     -   d) exposing identified or isolated bacteria of step c), or an         extract thereof, to one or several virus-producing cell types to         select bacteria which affect the production of virus or         viability of virus-infected cells.

The method may further comprise a step of isolating or purifying the anti-viral agent produced by said bacteria.

The methods of the present invention may also include a step of determining the genus/species of the identified or isolated bacteria. In this respect, the invention is particularly suited for identifying or isolating Deinococcus bacteria which produce a selected metabolite.

Accordingly, in a particular embodiment, the invention relates to a method for identifying or isolating a bacterium which exhibit a selected activity (e.g. which produces a metabolite of interest), the method comprising:

-   -   a) providing a sample comprising uncharacterized bacteria;     -   b) subjecting the sample to a cell destructing DNA damaging         treatment, preferably a repeated irradiation treatment;     -   c) identifying or isolating living or growing Deinococcus         bacteria from said treated sample; and     -   d) selecting Deinococcus bacteria of step c) which exhibit the         selected activity.

The bacteria can be characterized and classified e.g., according to Hirsch, 2004 and Kampfer, 2008. The physiological characterization includes for instance the determination of the fatty acid, respiratory quinones, polar lipids and polyamines patterns, a metabolic profiling of different sources of carbon and/or the determination of the 16S rDNA gene sequences.

Furthermore, the methods of this invention can comprise one or several additional steps of selecting bacteria having particular properties. More particularly, in a preferred embodiment, the method further comprises one or several steps of selecting bacteria which are viable or grow under selected culture conditions, such as media, temperature, pH, salinity, nutrients, oxygenation or carbon source. For this purpose, the sample or bacteria can be placed under appropriate selection conditions during any one of steps b), c) or d), or during a prior or subsequent step, and the resulting property is selected for during any of these steps.

In a particular aspect of the present invention, the bacteria are cultured under particular temperature conditions in order to identify or isolate bacteria which are viable or can be grown in a temperature range from approximately 4 to 70° C. More particularly, the bacteria are maintained at the selected temperature during step b), c) and/or d); and/or during an additional step e), in order to identify or isolate bacteria which are viable or can be grown at the desired temperature.

In another particular aspect of the present invention, the bacteria are cultured under particular saline conditions in order to identify or isolate bacteria which are viable or can be grown under concentration conditions of NaCl or equivalent salts possibly reaching around 5% weight/volume. More particularly, the bacteria are maintained at the selected salinity during step b), c) and/or d), and/or during an additional step e), in order to identify or isolate bacteria which are viable or can be grown at the desired salinity.

In a further particular and preferred embodiment of the present invention, the bacteria are cultured under particular pH conditions in order to identify or isolate bacteria which are viable or can be grown in a pH interval between approximately 3 and 9.5, preferably between 4 and 8. More particularly, the bacteria are maintained at the selected pH during step b), c) and/or d); and/or during an additional step e), in order to identify or isolate bacteria which are viable or can be grown at the desired pH.

In a further particular embodiment of the present invention, the bacteria are cultured under particular oxygenation conditions in order to identify or isolate bacteria which are viable or can be grown in aerobic and/or anaerobic conditions. More particularly, the bacteria are maintained under the selected oxygenation conditions during step b), c) and/or d); and/or during an additional step e), in order to identify or isolate bacteria which are viable or can be grown at the desired conditions.

In a further particular embodiment of the present invention, the bacteria are cultured in a particular culture medium in order to identify or isolate bacteria which are viable or can be grown in the presence of a selected carbon source. More particularly, the bacteria are maintained under the medium during step b), c) and/or d); and/or during an additional step e), in order to identify or isolate bacteria which are viable or can be grown using the desired carbon source.

It should be understood that the above characteristics can be selected individually or in any combinations. For instance, the method can be used to identify bacteria which are viable or can be grown at a desired temperature and salinity, or at a desired temperature and pH, or at a desired temperature, pH and oxygenation condition.

Furthermore, the methods of this invention may comprise a further step of modifying, e.g., either biologically, genetically and/or chemically, the identified or isolated bacteria, or their DNA, by any process known per se in the art, said modification aiming e.g., to improve the viability, growth or functions of the said bacterium, e.g., in order to improve the antibiotic activity. Such modification step includes, without limitation, cell fusion, accelerated evolution, DNA shuffling, mutagenesis, insertion of eukaryote, prokaryote or synthetic nucleic acid (e.g., DNA) from another strain, or any genetic engineering technology. The modification may also include a step of introducing a marker gene (e.g., kanamycin resistance) in the bacterium.

Many (marketed) antibacterial drugs are semisynthetic analogs of natural products, and are obtained from modifications of initial fermentation products. This is the case for Ketolides, the β-lactam group of antibiotics. Semisynthesis or even manipulation of the enzymes involved in the antibiotic biosynthesis can therefore be used to improve the initial hit (Von Nusssbaum, 2006, Marsden, 1998).

Accordingly, in a particular embodiment, the invention resides in a method of producing a bacterium having a selected activity, the method comprising isolating a bacterium according to any of the above described methods and modifying said bacterium e.g., by genetic, biologic or chemical treatment to improve said activity.

As illustrated in the examples, the method of the present invention has allowed the efficient and rapid isolation of UV-resistant bacteria which produce secondary metabolites (e.g., antibiotics). These bacteria were unknown before and can extend the diversity and spectrum of antibiotic activity (or other secondary metabolites) for therapeutic or other industrial purposes.

A further aspect of this invention therefore also resides in a bacterium obtainable by a method as disclosed above, or an extract thereof. The extract may be any preparation derived from a cell culture, such as a supernatant, a lysate, a cell membrane, or enriched/purified preparations derived therefrom, preferably containing a secondary metabolite.

The bacterium may belong to different genus, such as, e.g., Bacillus, Methylobacterium, Sphingobacterium, Cellulosimicrobium, Tepidimonas, Nocardia, Deinococcus, Truepera, Porphyrobacter sp., Novosphingobium sp., Exiguobacterium sp., Chromobacterium sp, Arthrobacter sp, Rhodococcus sp, Microbacterium sp, Kineococcus sp, or Williamsia sp.

The invention also relates to a method of producing a recombinant host cell, the method comprising identifying or isolating or producing a bacterium according to any one of the methods as defined above and cloning genes (or gene clusters or operons, or corresponding synthetic or recombinant nucleic acids) from said bacterium into another host cell, thereby producing a recombinant host cell. The host cell may be a prokaryotic or eukaryotic host cell, preferably a prokaryotic host cell. Cloning can be made according to techniques known per se in the art, such as using cloning vectors (e.g., plasmids, phages, bacterial chromosomes, etc.). In a preferred embodiment, genes or gene clusters encoding all or part of a biosynthetic pathway (e.g., genes encoding enzymes involved in such pathways) are isolated from the identified bacterium, cloned into appropriate vectors, and inserted into the selected host cell, to build new biosynthetic pathways.

The invention also relates to a method of producing a pharmaceutical agent (such as an antibiotic), the method comprising identifying or isolating or producing bacterium according to any one of the above methods, wherein said bacterium produces the pharmaceutical agent, and producing said antibiotic. Production of the pharmaceutical agent may comprise culturing the bacterium (or progeny or derivatives thereof) under suitable conditions are collecting or purifying the agent. Production of the agent may also comprise artificial synthesis (e.g., chemical, recombinant, enzymatic, etc.).

A further object of this invention is a method of identifying, isolating or producing a pharmaceutical agent (such as an antibiotic), using a wild type Deinococcus bacterial strain.

A further object of this invention is a method of identifying, isolating or producing a pharmaceutical agent (such as an antibiotic), using a modified Deinococcus bacterial strain.

A further object of this invention resides in the use of a Deinococcus bacterium to produce a pharmaceutical agent (such as an antibiotic).

A further object of this invention is an antibiotic derived from a Deinococcus bacterium.

Also, the present invention can be used to select bacteria and to generate metagenomic libraries. Typically genomic DNA from such bacteria is extracted and large fragments of DNA are (directly) cloned in a shuttle vector to make a metagenomic library representative of said bacteria. This metagenomic library can be transferred into different host bacteria to identify secondary metabolite producing strains. As an example, enzymes responsible for polyketide production can be screened according to Ginolhac, 2007.

Furthermore, the invention also relates to improved industrial methods of using microorganisms. Indeed, the invention also proposes to include one or several cell destructing DNA damaging treatments into industrial processes in order to eliminate potentially contaminating bacteria. Indeed, since bacteria of the present invention are able to grow and survive such cell-destructing treatments, the latter may be used, e.g., in any industrial fermentation or culture device or installation, to avoid contamination. In this respect, a particular object of this invention also resides in a process of using a bacterium obtainable by a method as described above in a fermentation or continuous culture, wherein the process comprises a step of irradiation of the bacterium prior to or following initiation of the fermentation or of the continuous culture, to limit contamination by other bacteria or cells. A further object of this invention is a process of using a Deinococcus bacterium in a fermentation or continuous culture, wherein the process comprises a step of irradiation of the bacterium prior to or following initiation of the fermentation or of the continuous culture, to limit contamination by other bacteria or cells. Irradiation may be performed repeatedly, typically under the conditions described above.

Further aspects and advantages of the instant invention will be disclosed in the following examples, which should be regarded as illustrative and not limiting. All references (patent applications, patents, scientific publications) cited in this application are incorporated therein by reference.

EXAMPLES Example 1 Determination of Improved Conditions for Selecting Metabolite-Producing Bacterium

In a preliminary step, 5 strains were tested for their resistance to UV. These strains were E. coli, Deinococcus radiopugnans, Deinococcus radiodurans, Deinococcus sp. and Deinococcus geothermalis.

Stationary phase cultures of the 5 tested strains were successively diluted from 10° to 10⁻⁸. All dilution were spotted (5 μL) on agar rich media TGY (Trypton 10 g/l, Glucose 2.5 g/L and Yeast extract 5 g/L) and different UV-treatments were applied: 0 mJ/cm², 4 mJ/cm², 17 mJ/cm², 42 mJ/cm² and 167 mJ/cm² with a BioLink crosslinker (Vilbert Lourmat).

Table 1 below presents the bacterial density after different UV treatments.

TABLE 1 Strains 0 mJ/cm² 4 mJ/cm² 17 mJ/cm² 42 mJ/cm² 167 mJ/cm² D. radiopugnans (CFU/ml) 4.00E+09 1.00E+09 1.60E+08 6.00E+05 0.00E+00 D. radiodurans (CFU/ml) 2.00E+07 6.00E+06 2.00E+06 2.00E+03 0.00E+00 E. coli (CFU/ml) 3.00E+07 2.00E+04 0.00E+00 0.00E+00 0.00E+00 D. geothermalis (CFU/ml) 1.20E+09 6.00E+08 8.00E+05 0.00E+00 0.00E+00 Deinococcus sp. (CFU/ml) 8.00E+08 2.20E+08 6.00E+06 4.00E+03 0.00E+00

As can be seen, a treatment of 4 mJ/cm² reduces by 3 log the bacterial titer in a culture of E. coli. A treatment of 17 mJ/cm² also discriminates between E. coli and Deinococcus bacteria.

In a second step, a soil suspension was subjected to different irradiation treatments based on the results of table 1. The soil suspension was prepared as follows: 5 g of wet soil was diluted in 20 mL distilled water. After vortex and sonication (1 minute), soil supernatant was collected and mixed with a 350 μL D. radiopugnans culture in stationary growth phase. An aliquot (50 μL) was spread on TGY agar containing an antifungal (cycloheximide, 100 μg/mL), and different repeated sequential irradiation treatments were tested: 1 treatment, 2 treatments and 3 treatments. 4 h-intervals was respected between each UV treatment.

FIG. 1 a shows the results obtained after one exposure at 0 mJ/cm², 4 mJ/cm² and 17 mJ/cm². FIG. 1 b shows the results obtained after 1, 2 and 3 exposures to 4 mJ/cm².

As can be seen, the best tested conditions are 3 exposures to UV irradiations of 4 mJ/cm² each. Such conditions provide the highest amount of growing Deinococcus bacteria from the treated soil sample. A substantial amount of Deinococcus bacteria is also obtained after one exposure of the sample to UV irradiation of 17 mJ/cm².

Example 2 Isolation of UV-Resistant Bacteria from Water Samples

Water samples were concentrated by filtration over a 0.22 μm nitrocellulose filter (Millipore, France), then placed in suspension in 10 ml of sterile water. The filtered solution is then sonicated for approximately 60 seconds to resuspend the bacteria.

Following sonication, between 150 μl and 2 ml of the suspensions are spread on a solid PGY-agar enriched culture medium sterilized by autoclaving (20 minutes at 120° C.) containing glucose (Sigma-Aldrich, France) 1 g/l, peptone (Fluka, France) 10 g/l, and yeast extract (Fluka, France) 5 g/l. The seeded culture then undergo 3 UV treatments of 4 mJ/cm² each using a BLX-E254 biolink (Vilber-Lourmat, France), carried out at an interval of 4 hours. After incubation at 30 to 50° C. for 3 to 4 days, the viable colonies of interest were visible.

Examples of colonies identified are listed in Table 2 below.

Example 3 Isolation of UV-Resistant Bacteria from Wood and Pebble Samples

Wood and pebble samples were immersed in sterile water then vortexed and sonicated for approximately 60 seconds.

Following sonication, between 150 μL and 2 ml of the suspensions are spread on a solid PGY-agar enriched culture medium sterilized by autoclaving (20 minutes at 120° C.) containing glucose (Sigma-Aldrich, France) 1 g/l, peptone (Fluka, France) 10 g/l, and yeast extract (Fluka, France) 5 g/l. The seeded culture media then undergo 3 UV treatments using a BLX-E254 biolink (Vilber-Lourmat, France) of 4 mJ/cm2 each, carried out at an interval of 4 hours. After incubation at 30 to 50° C. for 3 to 4 days, the viable colonies of interest were visible.

Examples of colonies identified are listed in Table 2 below.

Example 4 Isolation of UV-Resistant Bacteria from Stones, Moss, Lichen, Mud, Sediment, Biofilm, Soil and Animal Dejection

Samples of moss, lichen, mud, soil and animal dejection were placed in suspension in sterile water (V/V) then vortexed. The samples were then sonicated for approximately 60 seconds.

Following sonication, between 150 μL and 2 ml of the suspensions are spread on a solid PGY-agar enriched culture medium sterilized by autoclaving (20 minutes at 120° C.) containing glucose (Sigma-Aldrich, France) 1 g/l, peptone (Fluka, France) 10 g/l, and yeast extract (Fluka, France) 5 g/l. The seeded culture media then undergo 3 UV treatments using a BLX-E254 biolink (Vilber-Lourmat, France) of 4 mJ/cm2 each, carried out at an interval of 4 hours. After incubation at 30 to 50° C. for 3 to 4 days, the viable colonies of interest are visible.

Examples of colonies identified are listed in Table 2.

TABLE 2 Isolation Biotope Genus t ° C. Pebble Bacillus 30° C. Stones Methylobacterium 30° C. Animal dejection Sphingobacterium 30° C. Stones Cellulosimicrobium 30° C. Water Tepidimonas 45° C. Water Deinococcus 45° C. Pebble Deinococcus 30° C. Muck, pebble, soil Chromobacterium 30° C.

Example 5 Isolation of Bacteria from Bleocin-Treated Samples

Soil samples containing Deinococcus radiopugnans strain DRH40 were placed in suspension under conditions similar to that of example 2. In place of irradiation, the suspensions were maintained in the absence (control) or presence of 50 μg/ml or 100 μg/ml of bleocin.

In the absence of bleocin, no growing pink colonies (Deinococcus) are observed, but only indigenous microflora. In the presence of 50 μg/ml bleocin, indigenous microflora decreases drastically, and pink colonies are present. The same phenomenon is observed at 100 μg/ml of bleocin.

Example 6 Identification of Antibiotic Producing Bacteria

The UV resistant strains as disclosed in Table 2 were tested for their ability to inhibit the growth of several reference strains of bacteria. Briefly, fermentation was carried out in 10 ml PGY medium containing peptone 5 g/L, yeast extract 2.5 g/L and, glucose 0.5 g/L at 30 to 50° C. with aeration and agitation. After 3 days the antibiotic production of the tested strains was controlled and quantified by diffusion test agar against several reference strains cultivated on LB medium.

-   -   LB: Bacto-tryptone 10 g/L, Yeast extract 5 g/L, Sodium chloride         10 g/L     -   PGY: peptone 5 g/L, yeast extract 2.5 g/L, glucose 0.5 g/L,     -   Reference strains:         -   Staphylococcus aureus CIP 76.25         -   Escherichia coli CIP 76.24;         -   Candida tropicalis CIP 1275.

The results are depicted in Table 3 below.

TABLE 3 Tested Staphylococcus Escherichia coli Candida tropicalis Bacteria aureus CIP 76.25 CIP 76.24 CIP 1275 Strain 1 0 + + Strain 2 + + 0 Strain 3 0 0 0 Strain 4 + 0 0 Strain 5 + 0 0 Strain 6 0 0 + Deinococcus 0 + 0 0: no visible antibiosis; +: visible antibiosis

The results show that several strains exhibiting antibiotic activity have been isolated. These strains produce antibiotic activity which is active against Staphylococcus aureus, Escherichia coli and/or Candida tropicalis. The producing strains are resistant to UV and can be grown at elevated temperature, thereby illustrating the efficacy of the method of this invention.

Example 7 Antibiotic Production Screening Assay

7.2. Material and Method

Culture Media

Different media were prepared to test antibiotic production. 100 mL of solution A is composed by MnCl₂, 4H₂O 0.1 g, ZnSO₄, 7H₂O 0.1 g and FeCl₃ 0.1 g.

Medium 1 is composed by bacto peptone from casein 5 g/L, bacto yeast extract 3 g/L and adjusted at pH 7.1.

Medium 2 is composed by cellobiose 10 g/L, K₂HPO₄ 1 g/L, MgSO₄, 7H₂O 1 g/L, NaCl 1 g/L, (NH₄)₂SO₄ 2 g/L, CaCO₃ 2 g/L and adjusted at pH 7.2. Solution A is added at 1 ml/L.

Medium 3 is composed by oatmeal 20 g/L and solution A at 1 ml/L.

Culture Preparation of Test Strains

Strains were inoculated in 5 mL of PGY liquid media. Precultures were then incubated at 30° C. or 45° C. for 48 hours under shaking at 150 rpm.

In 15 mL-glass tube, 100 μL of preculture were inoculated in 5 mL of media 1 to 3. Cultures were then incubated at 30° C. or 45° C. for 48 hours, 96 hours, 168 hours and 336 hours under shaking at 150 rpm.

Culture Preparation of Target Strains

Target strains were Staphylococcus aureus CIP76.25, Escherichia coli CIP 76.24, Pseudomonas aeruginosa CIP 76.110, Streptococcus pneumoniae CIP 104485 and Candida tropicalis DSM 1346.

They were cultivated on LB medium at 37° C. for 18 hours. Then, 10 mL soft agar (Luria Bertani medium with agar at 7 g/L) were inoculated at 2% (v/v) with preculture of target strains in a petri dish.

Evaluation of Antibiotic Production

After incubation at 30° C. or 45° C. for 48 hours, 96 hours, 168 hours and 336 hours, 1 mL-test culture was centrifuged at 13000 rpm for 3 minutes. The supernatant was then filtered on 0.22 μm-filter. 10 μL of filtered culture supernatant was inoculated on soft agar containing target strains. After incubation at 37° C. for 18 hours, lysis plaques could be observed.

7.2. Results

Table 4 presents example of different obtained antibiotic profiles. Kineococcus strain M10-5H produced antibiotics against Gram positive test strains and E. coli CIP 76.24. Deinococcus strain MC5-7F produced antibiotics against S. aureus CIP 76.25. Microbacterium strain MA3-7G produced antibiotics against C. tropicalis CIP 1275 and Williamsia strain MA3-6B produced antibiotics against Gram positive test strains and P. aeruginosa CIP 76.110.

TABLE 4 Results of antibiotic production tests Staphylococcus Streptococcus Pseudomonas Escherichia Candida aureus CIP pneumoniae aeruginosa coli CIP tropicalis 76.25 CIP 104485 CIP 76.110 76.24 CIP 1275 Kineococcus + + — + + M10-5H Deinococcus + — — — — MC5-7F Microbacterium — — — — + MA3-7G Williamsia + + + — — MA3-6B “+” means that an antibiosis has been observed. “—” means that no antibiosis has been observed.

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The invention claimed is:
 1. A method to identify or isolate from a sample a bacterium producing a pharmaceutical compound, the method comprising: a) providing a sample comprising uncharacterized and uncultivated bacteria; b) subjecting the sample to a repeated sequential irradiation treatment that is sufficient to reduce by at least 2 log the bacterial titer in a culture of E. coli, said treatment comprising at least 2 sequential irradiations at intervals of between 1 and 8 hours; c) identifying or isolating a living or growing bacterium having the ability to either reassemble its genome or to resist DNA damage, from said treated sample; and d) selecting a bacterium of step e) which produces the pharmaceutical compound.
 2. The method of claim 1, wherein the sample is an environmental sample.
 3. The method of claim 1, wherein said treatment comprises repeated irradiations selected from UV-, gamma- and/or X ray-irradiation(s), either alone or in combination.
 4. The method of claim 1, wherein the treatment comprises subjecting the sample to 2 to 5 UV treatments of between 0.5 and 400 mJ/cm² carried out at an interval of between 1 and 8 hours.
 5. The method of claim 1, further comprising a step of selecting a Deinococcus bacterium.
 6. The method of claim 1, wherein step b) is performed in a solid culture medium.
 7. The method of claim 1, wherein, in step c), colonies are identified or isolated.
 8. The method of claim 1, wherein steps c) and d) are performed sequentially, in any order, or simultaneously.
 9. The method of claim 1, wherein step d) comprises exposing identified or isolated bacteria of step c) to one or several indicator cells and selecting a bacterium which affects the viability, growth, metabolism, mobility, RNA expression, protein expression, protein secretion or virus production of at least one of said indicator cells.
 10. The method of claim 1, wherein the method comprises a further step of isolating or purifying said pharmaceutical compound.
 11. A method of producing a pharmaceutical compound selected from an antibiotic or bacteriostatic or anti-fungal or anti-parasitic or anti-viral or anti-metabolite or chemotherapeutic agent or a cytokine-activity compound or cell growth factor, the method comprising identifying or isolating a pharmaceutical compound-producing bacterium according to the method of claim 1 and producing said pharmaceutical compound.
 12. A method of producing a recombinant host cell, the method comprising identifying or isolating a bacterium according to the method of claim 1, and cloning one or several genes from said bacterium in another host cell to produce a recombinant host cell.
 13. The method of claim 1, wherein the repeated sequential irradiation treatment comprises three UV treatments of 4 mJ/cm² carried out at an interval of 4 hours.
 14. The method of claim 1, wherein the pharmaceutical compound is selected from antibiotics, bacteriostatic compounds, anti-metabolite, chemotherapeutic compounds, anti-parasitic agents, anti-fungal agents, anti-viral compounds, cytokine-activity compounds or cell-growth factors.
 15. The method of claim 14, wherein said pharmaceutical compound is an antibiotic.
 16. The method of claim 15, wherein said antibiotic inhibits the growth of Staphylococcus aureus.
 17. The method of claim 15, wherein said antibiotic inhibits the growth of Candida tropicalis.
 18. The method of claim 15, wherein said antibiotic inhibits the growth of Escherichia coli.
 19. The method of claim 15, wherein said antibiotic inhibits the growth of Streptococcus pneumoniae.
 20. The method of claim 15, wherein said antibiotic inhibits the growth of Pseudomonas aeruginosa. 